On trialkyl sulfonium salts of triiodomercury(II) and structure of the trimethyl salt

1247-1250The salt, [Me3S][HgI3], is a text book example of the relatively rare phenomenon of tricoordination among transition metal complexes of simple ligands. It was structurally characterized decades after P C Rây’s formulation of the [R3S] [HgI3] family of salts in 1930. We now report its structure at low temperature (150 K). The [Me3S]+ and [HgI3]- ions are respectively pyramidal and trigonal planar. The span of the three Hg-I distances and the three I-Hg-I angles are 2.69-2.74 Å and 110-125o respectively. The Hg atom is 0.12 Å displaced from the plane of the iodine atoms. Weak supramolecular Hg---I interactions among adjacent molecules are present in the lattice and these influence the trend of bond lengths and angles in the [HgI3]- ion. The S-C distances and C-S-C angles in the cation span the ranges 1.75-1.81 Å and 100-103o respectively